K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities
Abstract
We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in sub-Neptune-sized ({2.49}-0.24+0.34 {R}\oplus ) planet (K2-66b) with a mass of 21.3+/- 3.6 {M}\oplus . Because the star is evolving up the subgiant branch, K2-66b receives a high level of irradiation, roughly twice the main-sequence value. K2-66b may reside within the so-called “photoevaporation desert,” a domain of planet size and incident flux that is almost completely devoid of planets. Its mass and radius imply that K2-66b has, at most, a meager envelope fraction (<5%) and perhaps no envelope at all, making it one of the largest planets without a significant envelope. K2-106 hosts an ultra-short-period planet (P = 13.7 hr) that is one of the hottest sub-Neptune-size planets discovered to date. Its radius ({1.82}-0.14+0.20 {R}\oplus ) and mass (9.0+/- 1.6 {M}\oplus ) are consistent with a rocky composition, as are all other small ultra-short-period planets with well-measured masses. K2-106 also hosts a larger, longer-period planet ({R}{{p}} = {2.77}-0.23+0.37 {R}\oplus , P = 13.3 days) with a mass less than 24.4 {M}\oplus at 99.7% confidence. K2-66b and K2-106b probe planetary physics in extreme radiation environments. Their high densities reflect the challenge of retaining a substantial gas envelope in such extreme environments.
- Publication:
-
The Astronomical Journal
- Pub Date:
- June 2017
- DOI:
- 10.3847/1538-3881/aa725f
- arXiv:
- arXiv:1705.03491
- Bibcode:
- 2017AJ....153..271S
- Keywords:
-
- planetary systems;
- planets and satellites: detection;
- planets and satellites: dynamical evolution and stability;
- planets and satellites: formation;
- techniques: radial velocities;
- techniques: spectroscopic;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 14 pages, 8 figures, 5 tables, Accepted to AJ